DDO68 C: the actual appearance of a ghost satellite dwarf through adaptive optics at the Large Binocular Telescope

TL;DR

This study used adaptive optics imaging at the Large Binocular Telescope to resolve individual stars in the gas-rich dwarf galaxy DDO68 C, revealing its interaction with DDO68 and providing insights into its distance, stellar population, and low metallicity.

Contribution

First direct resolution of stars in DDO68 C using adaptive optics, clarifying its nature and interaction with DDO68 despite observational challenges.

Findings

DDO68 C is at approximately 13 Mpc distance, same as DDO68.

DDO68 is interacting with three satellites, including DDO68 C.

Results support DDO68's status as a low-mass, metal-poor dwarf galaxy.

Abstract

Through adaptive optics (AO) imaging with the SOUL+LUCI instrument at the Large Binocular Telescope we were able to resolve, for the first time, individual stars in the gas-rich galaxy DDO68 C. This system was already suggested to be interacting with the extremely metal poor dwarf DDO68, but its nature has remained elusive so far because of the presence of a bright foreground star close to its line of sight, that hampers a detailed study of its stellar population and distance. In our study, we turned this interloper star into an opportunity to have a deeper insight on DDO68 C, using it as a guide star for the AO correction. Although the new data do not allow for a direct distance measurement through the red giant branch tip method, the combined analysis of the resolved-star color-magnitude diagram, of archival GALEX FUV and NUV photometry, and of H$\alpha$ data provides a self-consistent picture in which DDO68 C is at the same $\sim$13 Mpc distance as its candidate companion DDO68. These results indicate that DDO68 is a unique case of a low mass dwarf, less massive than the Magellanic Clouds, interacting with three satellites (DDO68 C and two previously confirmed accreting systems), providing useful constraints on cosmological models and a potential explanation for its anomalous extremely low metallicity.